In conventional wireline and slickline operations, a workstring with different tools is lowered into casing, tubing or other tubulars in a borehole from a wire or cable spooled from a drum at surface. Wireline and slickline operations can be performed for many reasons during completion, maintenance and servicing, installation and retrieval of downhole apparatus, intervention and for well logging. Most strings of wireline tools comprise one or more devices that e.g. collect data from the well-bore concerning the characteristics of recovered fluids etc such as temperature, salinity etc, or perform other functions. In addition to suspending the string of tools, the wire or cable may also act as a conduit for power required by the tools to carry out their functions in the well-bore, and may include signal cables for conveying data gathered by the downhole sensors back to surface.
Wireline strings operate satisfactorily in vertical and near vertical wells, but problems arise when they are used in deviated wells, because when the well deviates beyond about 55xc2x0, the suspended string of tools no longer penetrates satisfactorily under gravity, as the frictional forces retarding it exceed the gravitational forces propelling it. Also, the string tends to snag on the tubular connections or other upsets on the inner wall of the casing.
According to the present invention there is provided a downhole device for incorporation into a downhole string and movement in a well-bore, the device comprising means to orient the device in a well-bore, and one or more conveying means arranged on the device to engage the inner surface of the well-bore.
The device can comprise a downhole sub for incorporation into a string or tool. The means to orient the device or sub can be eccentric means such as an eccentric weight or shape to the sub or a portion thereof. Typical eccentric orientation means can be ballast means such as a weight eccentrically positioned in the sub to favour adoption by the sub of one or more orientations rather than others. Typically the orientations favoured are those in which the conveying means are in contact with the inner surface of the well-bore. However, in other embodiments of the invention, the means for orienting the sub can be an external shape of the sub or a portion thereof e.g. an egg or oval shape that favours orientation of the sub on a wider portion of the sub than on a narrow portion e.g. at the tips of the oval. In that embodiment the conveying means can be associated with the wider portion of the sub so that they are brought into contact with the well-bore surface when the sub orientates itself on the wider portions of the sub.
The conveyors can be wheels, rollers or similar, but other types of conveyors can equally be useful, for example skis, endless tracks etc. Anything that reduces the frictional coefficient of the device is suitable for basic embodiments of the invention. It is preferred that the conveying means are provided in pairs in a side-by-side arrangement and that several pairs of conveying means are provided on the device or tool as a whole. The wheels or other conveyors etc are typically provided on the lower surface of the sub i.e. the lower surface when it has been oriented by the ballast.
The device can be made up into a tool or tool string, but can be incorporated into other strings to reduce frictional resistance to movement of the tool string in the well.
In a second aspect the invention also provides a downhole device for incorporation into a tool or work string and movement in a well-bore, the device having friction reducing means on its outer surface to facilitate passage of the device through a well-bore.
The friction reducing means can comprise the conveying means of the first aspect of the invention and the sub of the second aspect can also incorporate orientation means in certain embodiments.
A motor can be provided optionally in a separate module in the sub body. The motor can be powered by a battery also contained within a separate module in the sub.
The sub, tool or string in which it is incorporated may have a vibrator or oscillator which may typically be in the form of an eccentric rotor that can be rotated by the motor. The motor can drive either or both of the vibrator and the conveyor, and need not drive both even when both are provided in a particular embodiment. The vibrator typically induces vibrations in the tool body at a desired frequency, which may optionally be varied e.g. by adjusting mass or position of weights on the rotor or its rpm, or other vibration means.
The sub, tool or string in which it is incorporated may have a sensor coupled to a switch for controlling the motor and/or the vibrator. The sensor may be adapted to sense one or more characteristics of the tool or its environment. One preferred characteristic that the sensor can detect is the attitude of the sub or tool. For example, in a preferred embodiment, the sensor detects the vertical attitude of the sub or tool and sends a signal to the motor and/or the rotor to function if the sub or tool body deviates more than a fixed amount beyond the vertical. This automatically switches on the motor to drive the wheels and/or the vibrator when the sub or tool encounters a deviated well which might tend to retard the progress of the sub or tool through the well-bore. A typical deviation that can be chosen to activate the sensor is approximately 50xc2x0 to 75xc2x0. Thus, when the sub or tool enters a region of the well-bore which is deviated, say, by 70xc2x0, the sensor detects the deviation in the attitude, and as the sub or tool enters the deviated well-bore, the motor drives the wheels or the vibrator to reduce the friction of the sub or tool against the well-bore inner surface and avoiding or reducing the possibility of retarding the sub or tool on the inner surface of the well-bore.
The wheels or other conveyors are preferably disposed in side-by-side relationship and are arranged to contact the well-bore inner surface at or very near the circumference of the sub or tool. For example, in preferred embodiments, the wheels do not protrude substantially beyond the outer circumference of the body of the sub or tool, so that they substantially coincide with the outer circumference of the cylindrical body. Typically they extend through cut-away sections of the side-walls of the body, and follow the shape of the outer diameter of the body and/or the inner surface of the well-bore. The side-walls of the cylindrical body are typically formed with slots etc from which the wheels or other conveyors protrude very slightly so as to engage the inner surface of the well-bore. In preferred embodiments, the slots match the protruding portions of the wheels etc very closely, so as to avoid or minimise flat areas where the sub or tool can rest on the inner surface of the well-bore without contacting the well-bore inner surface with the wheels or other conveyors. The well-bore-engaging surfaces of the wheels are typically shaped to conform to the inner surface of the tubular through which the sub will be run.
In one preferred embodiment of the invention the wheels are of large diameter and are arranged to extend through the body of the sub at opposite sides, so that each wheel extends through opposing sides of the body and contacts opposing sides of the well-bore. Larger wheels can be more resistant to wear downhole, and can also reduce frictional coefficients. Typically the large wheels are positioned in pairs side-by-side, with each pair on the same axis through the sub.
In the above embodiments each wheel can be arranged on a central axle to extend through opposite sides of the sub, so that one large diameter wheel, or one side-by-side pair of wheels, can suffice. In some other preferred embodiments of the invention with wheels extending through opposite sides of the sub, smaller wheels are used with each wheel only extending through a single side to contact the well-bore surface only at one point, and typically wheels on opposing sides are mounted on different axles and optionally at the same axial position along the sub, so that an axial core can be provided for a power or data cable.
The various components of the sub or tool of the invention can optionally be provided in separate subs.
The sub or tool can therefore comprise a train of connected subs each having one or more wheels or rollers, batteries, motors, vibrators, sensors, knuckle or swivel joints.